Boulder Opal Facts, Information and Description

The gemstone Opal is the official October birthstone
as adopted by the American National Association of Jewelers
in 1912. It is also the birth stone for the Zodiac sign of
Libra. See the birthstone
tables for additional references to this stone.

Boulder opal is found in Australia where precious
opal forms in veins and patches within brown ironstone boulders.
When the opal is mixed through the ironstone it is called
matrix opal. Hardness ranges between 5.5 and 6 on the Mohs
scale.

Boulder opal is very durable due to the ironstone backing
the opal forms on. Because water content within
the opal is very low it almost never cracks or crazes as it
ages.